1. Field of the Invention
This invention relates to a power source failure detecting system for automotive control systems such as for power train control, running control or the like.
2. Description of the Prior Art
There has been in wide use electronic control technics in vehicles due to remarkable improvement in performance of semiconductor devices such as a microcomputer. For example, an electronic engine control system for controlling emission and improving fuel economy, an electronic control system for controlling the driving system of a vehicle, an electronic control system for controlling behavior of a vehicle and the like have been put into practice. Further, also in a four-wheel steering system in which both the front wheel and the rear wheels are turned in response to operation of the steering wheel, a control system utilizing a microcomputer is used for controlling the rear wheel steering characteristics, e.g., the rear wheel turning angle ratio, i.e., the ratio of the rear wheel turning angle to the front wheel turning angle which may be changed according to various conditions such as the vehicle speed, the steering angle turning ratio or the like. Various methods of controlling the rear wheel steering characteristics in the four-wheel steering system are disclosed in U.S. Pat. No. 4,572,316, and Japanese Unexamined Patent Publication Nos. 59(1984)-128054 and 60(1985)-16369, for example.
In such electronic control systems for a vehicle, the mechanism-to-be-controlled is generally controlled to the safety side in case of failure of sensors, circuits or the like in the control system. Particularly, in mechanisms having an electronic circuit, the power source system must be stably operated in order for the electronic circuit to function normally. However, in the case of the automotive control devices, the power source system is mainly formed of a battery and an alternator, and includes unstable factors unlike the commercial power source, and accordingly, it is necessary to provide a power source failure detecting system for detecting failure of the power source system and to immediately control the mechanism-to-be-controlled to the safety side upon occurrence of failure in the power source system. However, it will be inconvenient if the power source failure detecting system is so oversensitive as to respond to a temporary failure of the power source which can soon be recovered.